Developer of upcoming Xbox One title Happy Wars has revealed that yesterdays release of the game on the Xbox Store was a mistake. Full statement from their facebook page below:

URGENT NOTICE REGARDING THE MISTAKEN RELEASE OF HAPPY WARS for XBOX ONE

Greetings to all fans of Happy Wars and thanks for your great support.

Just now, a system glitch resulted in accidental early release of Happy Wars for Xbox One in the Xbox One Game Store.

IMPORTANT: Please note that after playing Happy Wars for Xbox One, the current version of Happy Wars for Xbox 360 will no longer be playable.
Official release of Happy Wars for Xbox One is planned in the near future, so please refrain from installing and running Happy Wars for Xbox One until that time.

The issue of Happy Wars for Xbox 360 becoming unplayable will be resolved by the next title update of Happy Wars for Xbox 360. However, if you have already installed and played Happy Wars for Xbox One, we sincerely apologize for the inconvenience this has caused you.

We will issue a further announcement regarding the official release date of Happy Wars for Xbox One, the official release date of the next title update of Happy Wars for Xbox 360, and information for users who may already have installed and played Happy Wars for Xbox One. Thank you for your patience and understanding.

Once again, we understand that this has been a serious inconvenience for our users, and we sincerely apologize.

Note: Edited about playing Happy Wars for Xbox 360 after played Happy Wars for Xbox One.